Earlier apparatus for extracting water from carpets are based on the principle that a liquid introduced into the carpet for removing dirt from the carpet, e.g. a shampoo, is removed by blowing air through the carpet pile, in a manner corresponding to dust discharge in conventional dust exhausters(e.g. vacuum cleaners). For blowing through the wet carpet such equipment may also use, instead of means for evacuating the liquid/air mixture by suction, compressed air to displace the liquid/air mixture from the carpet (cf, for example, the equipment for extracting water from carpets illustrated in West German Offenlegungsschrift No. 24 14 661).
By contrast with conditions for the removal of dust/air mixtures, in the case of liquid/air mixtures the shape of the discharge duct results in a smooth pattern of discharge as a result of the mutual cohesion force of the water droplets and gravitational force. Generally speaking, no attention has hitherto been devoted to this aspect in the construction and design of discharge ducts. In many cases the liquid/air mixture is collected - after it has left the carpet via a necessarily slot-like elongate outlet--in an obliquely upwardly-directed duct. However, the deflection of the air/water mixture led away from the initially horizontal lateral guide into a central discharge duct of relatively great cross-section creates unnecessary resistance forces. These resistance forces are further increased due to the fact that, in the discharge duct, the water is not removed in a uniform mixture with air but continues to flow back until the effective duct cross-section has so narrowed that large quantities of liquid are entrained, with some degree of force, i.e. the liquid "gulps". Very unfavorable flow conditions also occur when elongate narrow slot-like discharge ducts are used which, generally speaking, are extended vertically upwardly in an arcuate path of travel. The air flow follows the path of the least resistance, so that the greatest air speed is present in a flattened zone in the center of the cross-section viewed as a whole. The liquid in the air current is thrust towards both sides of the parallel slot and there meets the smallest air flow in the slot. The result is that the liquid flows laterally, particularly in the case of flat discharge ducts, and continues to accumulate at the lower duct end until the whole duct cross-section has become filled with liquid. The accumulated store of liquid, which fills out the duct, is periodically expelled in its entirety. This process is continuously repeated and has the result that not only is a gas flow pressure required which is sufficient to overcome the flow resistance in the carpet and at the walls of the discharge duct, but also that the pressure must be sufficient to raise the water the necessary height and also to overcome the resistance derived from the above-described backflow of the water.
For solving this problem a duct was developed for the apparatus described in Offenlegungsschrift No. 26 14 661. Here, the discharge duct is such that the liquid/air mixture is initially collected in a transverse duct and is laterally upwardly guided, by way of an arcuate hose having a large radius of curvature, to a circular collecting container. In this construction of the discharge duct the harmful backflow of liquid was in large measure eliminated, and a uniform discharge flow achieved by preventing any accumulation of the liquid in the duct. However, these advantages were achieved at the expense of a relatively long duct flow path, with deflections in the direction of flow, and through the provision of elaborate means for collecting the liquid.